The gameport device operates like the other Amiga devices.  To use it, you
must first open the gameport device, then send I/O requests to it, and
then close it when finished. See the "Introduction to Amiga System Devices"
chapter for general information on device usage.

The I/O request used by the gameport device is called IOStdReq.

    struct IOStdReq
    {
        struct  Message io_Message;
        struct  Device  *io_Device; /* device node pointer  */
        struct  Unit    *io_Unit; /* unit (driver private)*/
        UWORD   io_Command;       /* device command */
        UBYTE   io_Flags;
        BYTE    io_Error;         /* error or warning num */
        ULONG   io_Actual;        /* actual number of bytes transferred */
        ULONG   io_Length;        /* requested number bytes transferred*/
        APTR    io_Data;          /* points to data area */
        ULONG   io_Offset;        /* offset for block structured devices */
    };

See the include file exec/io.h for the complete structure definition.

 Opening The Gameport Device 
 Gameport Device Controllers 
 Closing The Gameport Device